Nature of Color
Light and Matter
- Differentiate between transparent, translucent, and opaque
- Colors of visible spectrum range from red (long wavelength) to violet (high frequency)
Primary Colors of Light
- Green, red, and blue mixed together give white light
- Red + green = yellow
- Green + blue = cyan
- Red + blue = magenta
- Yellow, cyan, magenta = secondary light colors
Secondary Light Colors
- Complementary colors = two light colors which form white light
- Examples: yellow + blue; cyan + red; magenta + green
- All of the above are examples of the additive process
Subtractive Process
- We see colors because some colors are reflected and some are absorbed (dyes and pigments are responsible for this)
- Example: White light incident on a tomato: the tomato absorbs the blue and green and reflects the red
More Examples of Colored Objects
- Red light incident on a red rose: rose appears red because red reflects to our eyes; leaves absorb the red and become warmer than the petals because no red pigment is contained in the leaves
- Green light on a red rose: petals look black because petals absorb the green since there is no red incident light to reflect back
- Yellow daffodil illuminated with red light appears red
- …illuminated with yellow appears yellow
- …illuminated with green appears green
- …illuminated with blue appears black
Why is the Sky Blue?
- Violet light is scattered the most (shortest wavelength) but our eyes are more sensitive to blue
- When more dust particles are present, lower frequencies are scattered more
- After a rain, sky appears more blue due to absence of dust
- At greater altitudes there are less particles and eventually where there are no particles, the “sky” is black
- Clouds are made of different sized clusters of water molecules, ranging from low to high frequencies – overall effect is a bright white cloud
Why are Sunsets Red?
- Red light is scattered the least, has the longest wavelength
- Lowest path from sun to earth is at sunrise and sunset, hence more red reaches at these times, rather than higher frequencies
- If dust is present, longer red wavelengths diffract producing even more red
Why is Water Blue-Green?
- Water molecules absorb infrared waves because they resonate to those frequencies
- Water molecules resonate weakly to visible red frequencies causing a gradual red absorption by water
- When red is removed from the white sunlight, greenish-blue remains
(source)